The invention relates in particular to cages for constant-velocity rotary ball joints, as are used for example in the automotive industry. These joints have a joint outer part and a joint inner part, in which a plurality of substantially longitudinally running ball races are provided. The balls are fitted between the joint outer part and the joint inner part for the purpose of torque transmission, the positioning of the balls being ensured by a cage arranged between the joint outer part and the joint inner part. The cage has a plurality of cage windows for the balls, so that their movement in the axial direction is restricted.
With regard to the various types of joint, the invention relates in particular to cages for the following joints:
Rzeppa joints, in which the direct control of the balls onto the angle-bisector plane is effected by meridionally running ball races with longitudinally offset center points of the races of the joint inner part and joint outer part.
Undercut-free UF joints, which follow substantially the same principle, the ball races are designed to be undercut-free as seen in the axial direction.
What are known as DO joints, in which spherical guide surfaces with axially offset centers of curvature on the inner and outer sides are provided on the cage, so that in the event of joint inclination, direct control of the cage and therefore indirect control of the balls onto the angle-bisector plane takes place. Joints of this type are designed with curved ball guideways as fixed joints and with ball guideways which run in a straight line as axially displaceable joints.
Finally, reference should also be made here by way of example to what are known as VL joints, which have races which are at least partially associated with one another in the joint outer part and joint inner part and do not run strictly in the longitudinal direction, but rather form an angle with one another and thereby effect direct control of the balls onto the angle-bisector plane and onto half the displacement path.
In all these known joints, the cages are permanently or at least from time to time in sliding contact with the surfaces of the inner and/or outer part of the joint located between the ball races. For reasons of wear, it is in this respect necessary for all the sliding surfaces on the joint outer part, the joint inner part and on the cage to be hardened.
With regard to the cage, there has hitherto been provision for hardening to be carried out in the region close to the surface, in order in particular to avoid wear phenomena caused by friction with the joint outer part and/or joint inner part. In particular in the automotive industry, it is at present being recognized that ever greater forces or torques need to be transmitted using these joints. This imposes particular demands in particular if the joint is not subject to purely axial stresses, but rather the force or torque is transmitted with an inclination angle. This is related in particular to the transmission of force from the balls to the cage. A ball is generally held in position by means of three contact points, namely one with the inner part, another one with the outer part and a third with the cage. As the inclination angle increases, the race forces acting on the ball increase, and these forces then have to be compensated for to a greater extent by means of the cage. This resultant cage force ultimately leads to torque limiting of the joint at relatively high inclination angles. On account of ever increasing market demands for increasing torques, this fact means that ever larger joints have been required.